The present invention relates to an inflatable, collapsible mandrel for use in constructing and fabricating filament wound vessels and tanks, and a method of constructing such a mandrel.
Methods of constructing filament wound vessels, tanks and containers are well known in the prior art. Typically, a rigid mandrel made of aluminum, resin impregnated and coated fiberglass or other high strengh, relative lightweight filament, or the like is prepared and mounted on a winding machine so that the mandrel may be selectively rotated. The surface of the mandrel is coated with an appropriate mold release solution and then wound with resin impregnated or coated filaments, such as glass, Kevlar, graphite, nylon or boron, for example, with the winding progressing from end to end, for an elongated mandrel, or from side to side, for a more spherical mandrel. When the desired thickness of the winding layers is achieved, the winding is stopped and the resin is cured.
The resulting filament wound vessel is removed from the mandrel by cutting the vessel circumferentially, at a location near the center thereof, to penetrate to the mandrel. The two halves of the vessel are then removed from the mandrel and the halves joined and bonded together to form the desired vessel or tank. A short helical wind of a resin coated filament strand or roving may be made over the joint of the vessel to further secure the two halves together.
Examples of prior art winding techniques and methods are disclosed in U.S. Pat. Nos. 3,386,872, 3,412,891, 3,697,352, 3,692,601, 3,533,869, 3,502,529 and 3,414,449.
Because of the joint in the completed vessel, an inherent weakness exists which may be the first to fail or fracture when the vessel is subjected to pressure or stress. It would be desirable for the shell of the vessel to be continuously wound with no breaks or joints to better preserve the integrity and strength of the structure and the ability of the structure to withstand stress. Providing a mandrel which somehow could be removed from the interior of the vessel without cutting the vessel would appear to provide a solution.